A cyclic carbonic ester is generally synthesized by condensing a diol or its reactive equivalent or synthon with carbonic acid or its derivative. For example, Japanese Patent Application Laid-open No. 235252/1997 (JP-A-9-235252) discloses a method for synthesizing a cyclic carbonic ester from oxyrane and carbon dioxide by ring expansion, and there is disclosed in the Encyclopedia of Reagents for Orgnaic Synthesis, vol. 6, p.4108 a method of synthesizing cyclic carbonic esters using a diol and phosgene. These methods, however, require the use of specific material, i.e., oxirane or phosgene, which is hard to obtain. Besides, oxirane is highly explosible and phosgene is of high toxicity and therefore dangerous and require handling with care. For such reasons, commercial operation according to the above methods has difficulties.
Synthesis of a cyclic ester from a diol and a carbonic ester has been known as one way to solve the problem of handling. For example, U.S. Pat. No. 2,441,298 discloses a process for synthesizing ethylene carbonate from ethylene glycol and diethyl carbonate using sodium metal as a catalyst. U.S. Pat. No. 3,663,569 discloses a process of synthesis using a dialkyl or aryl tin oxide as a catalyst, and U.S. Pat. No. 5,091,543 discloses a process of synthesis using an alkyl ammonium salt, tertiary amine, or an ion-exchange resin containing those as a catalyst. However, sodium metal as a catalyst has possibility of explosive reaction on contact with water, and handling with care is also needed. On the other hand, the dialkyl or aryl tin oxide, and alkyl ammonium salts, and the like are not the catalysts of general-purpose and are hard to obtain.
For a better handling-convenience or accessibility, Japanese Patent Application Laid-open No. 56356/1990 (JP-B-2-56356) proposes and discloses a process for producing cyclic carbonic esters by, with the aid of potassium carbonate as a catalyst, stirring trimethylolpropane and diethyl carbonate in a packed column and gradually vacuuming up the column while evaporating ethanol being by-produced. This literature says that 6-membered-ring cyclic esters are also obtainable (yield: 91%) by dissolving the reaction mixture in a mixed solvent of methylene chloride/dioxane (1:1), making the resultant mixture flow over a crosslinked polystylene beads polymer, evaporating the solvent under reduced pressure for preliminary purification, gradually feeding the preliminary-purified product dropwise into a flask having been heated to 220.degree. C. in advance under reduced pressure for distillation, and trapping the distillate with liquid nitrogen. This method, however, is disadvantageous in commercial terms because the reaction is effected in the packed column. Moreover, this method involves many steps such as reaction, solvent-evaporation, dissolution, absorption, solvent-evaporation and distillation and therefore troublesome and complicated.
U.S. Pat. No. 3,426,042 discloses a process of synthesis of cyclic carbonic esters from glycol and diethyl carbonate using sodium hydroxide as a catalyst. But this literature fails to refer to its yield, not describing in further detail. Further, Journal of American Chemical Society, vol. 68 (1946), p.783 discloses a process in which ethylene carbonate is formed from ethylene glycol and diethyl carbonate using potassium carbonate as a catalyst and from which a cyclic carbonic ester is isolated by crystallization. In this method, however, the yield of the object compound is low (51 to 55%) and such low yield is not sufficient for practical commercial operation. Furthermore, although the isolation by crystallization is effective for ethylene carbonate (melting point: 37 to 39.degree. C.), not all object compounds are covered by this method. In the case where the object product is a cyclic carbonic ester having a low melting point, for example, a 6-membered-ring cyclic carbonic ester (propylene carbonate), the isolation by crystallization is not effective due to the melting point as low as -55.degree. C., and rather difficult. A product having a low melting point can be isolated by distillation, for example, by flash evaporation or thin film evaporation. The distillation of the reaction product according to the above-mentioned method, however, leads to the hydrolysis or reverse reaction of the reaction product and thus results in the decomposition of the object compound. Particularly, the use of an optically active substance as a reactant leads to the loss of its optical activity and racemization thereof.